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Window Trim

Interior window molding does double duty, covering gaps while defining a style. Use this guide to understand what each part does and how all the pieces fit together

Trim Terminology

Illustration by Harry Campbell

Interior window molding does double duty, covering gaps while defining a style.

Use this guide to understand what each part does and how all the pieces fit together.

The Crown

Illustration by Harry Campbell

a) crown molding

Angles out from wall at top of window, adding dimension lacking in flat stock. Together with frieze board and cap, makes up entablature, a feature found in classical house styles, such as Georgian, Federal, and Greek Revival.

b) mitered return

Covers end grain as it carries profile to wall.

c) frieze board

Serves as base for attaching crown molding and cap. Its ends line up with outside edges of casing.

The Top Corner

Illustration by Harry Campbell

d) crosshead strip

Provides transition between head casing and frieze board.

e) mitered return

Covers end grain as it carries profile to wall.

The Side Casing

Illustration by Harry Campbell

f) side casing

Covers gap between side of window frame and wall.

g) backband molding

Adds depth and width to outside edges of casing. L-shaped to fit neatly over corners.

h) inside stop

Holds sash in window opening. Removing stops allows sash to be taken out for repair.

The Bottom Corner

Illustration by Harry Campbell

i) horn

Extends stool past casing and apron by 1 to 2 inches.

j) mitered return

The Windowsill

Illustration by Harry Campbell

k) stool

Hides gap between bottom edge of lower sash and top of windowsill outside.

l) apron

Provides visual support for stool. Ends line up with outside edges of casing. Aprons with a profile require mitered returns.

The Top

Illustration by Harry Campbell

m) cap

Covers top of crown.

n) head casing

Covers gap between top of window frame and wall.

The Square Cut Miter

Illustration by Harry Campbell

In many Victorian-era, Craftsman, and Colonial Revival homes, casing ends are cut square, then butted against either adjacent casing edges or corner rosettes, which are separate blocks slightly thicker and wider than casing stock. For this joint to work, casings must be symmetrical, not tapered.

o) rosette

p) square-cut joint